An apparatus for producing a single crystal is used to produce single crystals such as semiconductors, dielectrics and magnets according to the CZ method. The apparatus comprises a crucible, a heater and the like that are accommodated in a chamber, the crucible which is driven to rotate about its center, the heater which is arranged around the crucible, heats a polycrystalline raw material that is introduced into the crucible by the heater to obtain a polycrystalline melt, immerses a seed crystal that is attached at a lower end of a superior axis such as a wire into the polycrystalline melt, and grows a predetermined single crystal below the seed crystal by pulling the seed crystal upward at a predetermined speed with rotating the superior axis.
FIG. 4 shows an example of a schematic sectional view of a conventional apparatus for producing a single crystal 13 according to the CZ method. In FIG. 4, 1 shows the crucible that accommodates the polycrystalline raw material 2 and a cylindrical heater 3 made of graphite etc. is arranged in the outer periphery of the crucible. As needed, a bottom portion heat insulating material 4 is arranged below the crucible 1, and a cylindrical heat-insulating material 5 is arranged outside the heater 3. These are accommodated in a lower chamber 6 or an upper chamber 7.
Moreover, a leading passage 8 for pulling the single crystal is provided in the upper chamber 7.
In the case of producing the single crystal by using the foregoing conventional apparatus for producing a single crystal 13, the polycrystalline raw material 2 is melted with a resistance heating heater 3 that is made of graphite etc. and that is arranged around the crucible 1. However, there is a problem such that melting time becomes longer in proportion to an increase in a charging amount (a melting amount) with a larger diameter of crystal in recent years.
In addition, heat generated with the heater 3 is dissipated upward through the upper chamber 7 or the leading passage 8 for the single crystal, at the same time, heat is also dissipated from a surface of the melted raw material and the crucible through the upper chamber 7 or the leading passage 8, and these make time required for melting longer.
For example, in the apparatus for producing a silicon single crystal having a large diameter, melting the polycrystalline raw material needs an electric power of 200 to 300 kW/h and almost all its heat quantity are discharged from a water-cooled chamber wall to the outside. The apparatus therefore needs to maintain an appropriate temperature and suppress the heat quantity consumed into a surface of the wall in a hot zone.
In view of this, there is disclosed an apparatus for producing a single crystal that enables the melting time of the polycrystalline raw material to be shortened by comprising an auxiliary heating device with a lamp or a laser separately from the heater arranged around the crucible (for example, see Japanese Patent Laid-open (Kokai) No. H10-81595).
In addition to that, in order to prevent heat from emitting to an upper portion of the chamber, there are disclosed an apparatus for producing a single crystal in which a heat shielding plate is arranged above the crucible at the time of melting the polycrystalline raw material (see Japanese Patent Laid-open (Kokai) No. H10-158091), and in which a discoid reflecting material, which is made of a high melting point material such as Mo, W or Si, is arranged at the time of melting the polycrystalline raw material (see Japanese Patent Laid-open (Kokai) No. 2001-213691).